How to pause physics simulations
To the best of my knowledge you can't pause the playback of the particles via the physics system. 

In order to accomplish this effect, you need to:


render the original particle sequence with the standard timing
render extra shots of frozen particles with Camera 2 and then edit the shots together in the VSE


In order to do that you need a way to freeze the particles in time so that you can render out the Camera 2 shots.

You can do this by setting up the particles to use a DupliObject, and then using the "Make Duplicates Real" command (CTRL+SHIFT+A) on the correct frames. I found it helpful to also parent the frozen particles to a new parent object.



Here's what I did to accomplish this.


Set up your initial particle system and animation (I chose a 10
particle, 50 frame sequence for the test). You will need to set
particle duplication to an object or group of objects. If you just want
a small point, use a small sphere)
You may want to bake your particle sim to disk and then switch your
particle system to read from external to avoid the simulation
changing.
Move the timeline to the frame you want to freeze (let's choose frame 20)
Select the particle emitter and use "Make Duplicates Real" command (CTRL+SHIFT+A)
Snap cursor to emitter and create new object (empty, plane, etc).
We'll call this one Frame20Parent.
Hide the emitter. Select new particle duplicates, then parent them
to the Frame20Parent object with CTRL+P
(keep transformations)
Now, you can render out frames from your Camera 2 animation with the
particles frozen in place.




Please note: I've spaced out the duplicate groups for clarity, but you would have to keep them in the same location as the original emitter object so the particle locations would match.

If this solution does not work for your project, please provide additional requirements and I can amend the answer.